State of the Park Report for Valley Forge National Historical Park

Resource Brief – Discovery of the Bone Cave

Partial skull of Smilodon gracilis from the Port Kennedy Cave, Valley Forge National Historical Park, Montgomery County, Pennsylvania. This gracile sabertoothed cat was first described by paleontologist Edward Drinker Cope from material collected at the Port Kennedy Cave. The reconstructed skull length is about 12 inches.

One of the most important North American fossil deposits of the Great Ice Age was discovered at Valley Forge. In 1870, the Port Kennedy Cave or Bone Cave was discovered during limestone quarry operations that occurred in Valley Forge before it was protected as park land. The Bone Cave is not a true "cave," but rather a sinkhole that was briefly open to the surface during the Pleistocene epoch, approximately 750,000 years ago. While it was open, scores of creatures slid into it and met their deaths. Because it was only briefly open to the surface, this rare fossil deposit provides scientists with information about the climate and wildlife community present at one particular time.

Over 1,200 fossils representing 14 plant and 48 animal species were collected during excavations that occurred between 1870 and 1896, including several species that have not been found anywhere else on the planet. Reflecting the biases of the time, only a few insects and plants were collected, and many fragmentary specimens went uncollected. The most abundant large mammal fossils were from lesser short-faced bears, Hays' tapirs and striped skunks; however, the deposit also yielded fossils from mastodons, a saber-toothed cat species, a North American horse, and a new species of cheetah-like cat. The diversity of species found in the sinkhole provides evidence that the climate was warm or temperate and the landscape thickly wooded
by oaks, beech, and hickory trees. Scientists suggest the animals may have come together in the
forest to feed or drink, where some fell into the sinkhole and became trapped.

Infiltration of groundwater in the quarry slowed early fossil recovery efforts and the deposit was never fully excavated. Many water-damaged specimens also were lost during the early collection efforts. The quarry itself was filled in during the early 1900s with waste from the nearby Ehret Magnesium Manufacturing Company, burying the remaining fossils under some 40 feet of asbestos-containing materials. Today, most of the excavated fossils are housed at the Academy of Natural Sciences of Drexel University in Philadelphia but some of the original fossils are also on display in the park Visitor Center. In addition, casts have been made of a few select fossils and are used for education programs.